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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />II <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Hydraulic Analysis <br /> <br />An analysis of the hydraulic characteristics of Crystal Creek and <br />Dirty Woman Creek was performed in order to determine water surface <br />elevations for the 100-year flood on each stream, Bridge elevations and <br />sizes of openings were surveyed and measured in the field on March 3 and <br />4, 1986. This data was combined with cross-section data taken from a 5' <br />contour mapping of the Town of Monument (Ref. 5). This cross-section <br />data became the input data in the U,S, Army Corps of Engineers HEC-2 <br />step-backwater computer program. <br /> <br />The locations of the cross-sections are shown on the "Flooded Area <br />Maps" (see Plates 2 to 5) and the hydraulic data for the cross-sections <br />is displayed in Tables 1 and 2, <br /> <br />Roughness coefficients (Manning's "n" values) were also used as <br />HEC-2 input. Roughness values for Crystal Creek varied from 0,020 <br />(concrete portion) to 0,040 for the channel and from 0,025 to 0~045 for <br />the overbank areas, Roughness values for Dirty Woman Creek varied from <br />0,025 to 0,050 for the channel and from 0,025 to 0.050 for the overbank <br />areas. <br /> <br />The starting water surface elevations for the Crystal Creek <br />analysis were the elevations given for Monument Lake on Monument Creek in <br />the Flood Insurance Study for unincorporated E1 Paso County (Ref. 2) <br />since this is the starting point of the Crystal Creek study. The <br />starting water surface elevations for Dirty Woman Creek was critical <br />depth since the first cross-section is immediately downstream from a <br />bridge which would be overtopped during a flood, <br /> <br />The computed 100-year f1 ood is out 1 i ned on the "Flooded Area Maps", <br />plotted on the "Flood Profile" sheets, and tabulated in the "Cross-section <br />and Water Surface Elevation Data" tables (Tables 1 and 2), <br /> <br />Culvert capacities are sufficient to pass the 100-year flow at all <br />but two stream crossings. Both Beacon Light Road over Crystal Creek and <br />the Denver Road over Dirty Woman Creek are inadequately sized, This is <br />believed to be intentional as the backed up water temporarily floods only <br />unused barren 1 and and the peak f1 ows downstream from these roads are <br />attenuated to a certain degree during high frequency flooding events <br />(i. e, common f1 ood events), Shou1 d the 1 and upstream from either road be <br />developed, then attention would have to be paid to the area that would be <br />flooded and culvert size perhaps should be increased, <br /> <br />Flooded Areas <br /> <br />The areas covered by the 100-year flood are shown on Plates 2 <br />through 5, Further information with regards to flood elevations at <br />various locations is given in the following sections of this report, <br />Currently there are no buildings in the 100-year floodplains of either <br />stream, <br /> <br />An exami nat ion of the Flood Insurance Rate Map for un incorporated <br />E1 Paso County (Exhibit 2) shows that flooded areas along Monument Creek <br />do not include any lands within the present boundaries of the Town of <br />Monument. <br /> <br />6 <br />